JP4780348B2 - MIMO receiving apparatus and receiving method - Google Patents

Description

  The present invention relates to a MIMO receiving apparatus and a receiving method for performing multiple input multiple output (MIMO) communication in wireless communication in which wireless technology is used for communication, and more particularly, to a single carrier MIMO signal as a frequency domain signal. The present invention relates to a MIMO receiving apparatus and a receiving method that perform MIMO signal separation by frequency domain processing.

  High-speed data transmission is required in next-generation mobile communication wireless systems. As a technique for realizing this high-speed data transmission, MIMO (Multiple Input Multiple Output) multiplexing, in which data signals are transmitted from a plurality of transmitting antennas using the same frequency and the data signals are demodulated using a plurality of receiving antennas, is noted. Has been.

  FIG. 1 is a diagram illustrating a configuration example of a conventional MIMO transmission / reception system using MIMO multiplexing.

  In the MIMO transmission / reception system shown in FIG. 1, when the number of transmission antennas is M (M is an integer of 2 or more) and the number of reception antennas is N (N is an integer of 2 or more), the transmission side is the transmission apparatus 201 and the transmission antenna. 202-1 to 202-M, and the receiving side includes receiving antennas 203-1 to 203-N and a receiving device 204. By transmitting different data signals from the plurality of transmission antennas 202-1 to 202-M using the same frequency and receiving the data signals using the plurality of reception antennas 203-1 to 203-N, the transmission bandwidth High-speed data transmission proportional to the number of transmission antennas can be performed without increasing the number of transmission antennas. In the receiving apparatus 204, it is necessary to demodulate (signal-separate) each data signal transmitted from the plurality of transmitting antennas 202-1 to 202-M from signals received by the plurality of receiving antennas 203-1 to 203-N. .

  Various methods have been proposed for the MIMO signal separation. For example, a linear filter based on a minimum mean square error method (MMSE) is used as the simplest method, and a transmission antenna to be demodulated is used. There is a method for suppressing interference from other transmission antennas. However, the reception characteristics when this method is used are not good. In order to improve reception characteristics using this method, a method combining an MMSE filter and transmission antenna interference cancellation has been proposed.

  Further, a maximum likelihood detection method (MLD: Maximum Likelihood Detection) is considered in which replicas of all transmission antenna signals are generated and the most likely transmission antenna signal is selected. While this detection method has good reception characteristics, the amount of computation increases exponentially as the number of transmitting antennas and the number of modulation multilevels increase.

  On the other hand, in the uplink radio system of next-generation mobile communication, it is necessary to realize high transmission power efficiency in the terminal in order to expand the communication area, and a single peak-to-average power ratio (PAPR) is required. A carrier (SC: Single-Carrier) method is considered to be dominant. When MIMO multiplexing is performed in the SC system, multipath interference becomes a problem. In addition, when MIMO signal separation is performed using an MMSE filter, MIMO signal separation and multipath interference suppression are performed simultaneously, that is, a spatial and temporal MMSE filter (two-dimensional MMSE filter) is required. A method combining a two-dimensional MMSE filter and transmission antenna interference removal has excellent characteristics and is considered promising.

  FIG. 2 is a diagram illustrating a configuration example of a conventional MIMO receiving apparatus.

  In the MIMO receiving apparatus shown in FIG. 2, an increase in the amount of computation is suppressed by performing two-dimensional MMSE equalization and transmission antenna interference removal by frequency domain signal processing. In addition, a method for improving the characteristics by repeatedly performing the two-dimensional frequency domain equalization and the reception processing for removing the antenna interference has been considered (for example, the document “SC using two-dimensional MMSE weight for frequency domain repetition PIC”). -Throughput characteristics of MIMO multiplexing, "Akinori Nakajima, Fumiyuki Adachi, Shingaku Giho, RCS 2005-88, pp. 19-24, October 2005.).

  The MIMO receiving apparatus shown in FIG. 2 receives single carrier MIMO signals transmitted from M (M is an integer of 2 or more) transmission antennas by N (N is an integer of 2 or more) receiving antennas, A MIMO receiver that performs MIMO signal separation by frequency domain processing. This MIMO receiving apparatus includes receiving antennas 101-1 to 101-N, a cyclic prefix (CP) removing unit 102-1 to 102-N, and a discrete Fourier transform (DFT) unit 103-. 1 to 103-N, reception filters 104-1 to 104-N, a subtraction unit 105, a channel estimation unit 106, a weight calculation unit 107, a two-dimensional frequency domain equalization unit 108, and a discrete inverse Fourier transform ( IDFT (Inverse Discrete Fourier Transform) sections 109-1 to 109-M, bit likelihood calculation sections 110-1 to 110-M, symbol replica generation sections 111-1 to 111-M, and DFT sections 112-1 to 112-1 112-M and antenna interference replica production It is composed of a part 113-1 to 113-M.

  FIG. 3 is a diagram illustrating an example of a radio frame format when frequency domain equalization is used.

  The frame shown in FIG. 3 indicates a radio frame signal transmitted from a certain transmission antenna. The radio frame signal is composed of a plurality of blocks of pilot signals or data signals. In the example shown in FIG. 3, there is a pilot signal block at the head, and a plurality of data blocks are continued after that. A CP is added to the head of each block in order to avoid multipath interference from the previous block during DFT processing. CP is a signal generated by copying the last data of each block to the front. In MIMO, it is necessary to estimate the channel gain between the transmitting antenna and the receiving antenna, and the pilot signals of each transmitting antenna are preferably orthogonal to each other. As a multiplexing method of pilot signals of each transmitting antenna, frequency multiplexing using an IFDM (Interleaved Frequency Division Multiplexing) method, code multiplexing using a cyclic shifted CAZAC (Constant Amplitude Zero Auto-Correlation) code, and the like are considered. .

  In addition, the receiving antennas 101-1 to 101-N illustrated in FIG. 2 receive a single carrier MIMO signal. CP removing sections 102-1 to 102-N receive the respective reception antenna signals, and remove the signal corresponding to the CP at a common timing. The DFT units 103-1 to 103 -N each receive the received antenna signal from which the CP has been removed,

ポイントのＤＦＴを行い、受信信号を周波数領域に変換する。受信フィルタ１０４−１〜１０４−Ｎは、周波数領域で受信信号のフィルタリングを行い、波形整形、雑音抑圧、ユーザ分離などを行う。受信フィルタ１０４−１〜１０４−Ｎには、一般にレイズドコサインロールオフフィルタが用いられる。図２に示した構成では受信フィルタ１０４−１〜１０４−Ｎは、周波数領域の信号処理で行っているが、ＤＦＴ部１０３−１〜１０３−Ｎに先立ち時間領域の信号処理で行うこともできる。減算部１０５は、復調対象の送信アンテナ信号を残し、他の送信アンテナ干渉レプリカを減算する。

A point DFT is performed to convert the received signal into the frequency domain. The reception filters 104-1 to 104-N perform reception signal filtering in the frequency domain, and perform waveform shaping, noise suppression, user separation, and the like. Generally, raised cosine roll-off filters are used for the reception filters 104-1 to 104-N. In the configuration illustrated in FIG. 2, the reception filters 104-1 to 104-N are performed by frequency domain signal processing, but may be performed by time domain signal processing prior to the DFT units 103-1 to 103-N. . The subtracting unit 105 leaves the transmission antenna signal to be demodulated, and subtracts other transmission antenna interference replicas.

  FIG. 4 is a diagram illustrating a configuration example of the subtracting unit 105 for the DFT signal of the receiving antenna n.

  The subtracting unit 105 shown in FIG. 4 includes replica synthesizing units 121-1 to 121-M and subtractors 122-1 to 122-M. Replica synthesis sections 121-1 to 121-M synthesize transmit antenna interference replicas excluding demodulated transmit antenna signals. Subtractors 122-1 to 122-M subtract the outputs of replica synthesis sections 121-1 to 121-M from the DFT signal of reception antenna n.

  Subcarrier after DFT

の受信信号を

Received signal

とし、送信アンテナｍの第ｉ繰り返し干渉レプリカを

And the i th iterative interference replica of the transmitting antenna m

とすると、第ｉ繰り返し干渉除去後の送信アンテナｍの等化用信号

Then, the equalization signal of the transmission antenna m after the i-th repetitive interference cancellation

は次式で表される。

Is expressed by the following equation.

ここで、最初（第０繰り返し）の受信処理では干渉除去は行わず、受信信号をそのまま用いる。すなわち、

Here, in the first (0th iteration) reception process, interference is not removed and the received signal is used as it is. That is,

となる。

It becomes.

  Channel estimation section 106 estimates the channel gain between the transmission antenna and the reception antenna in the frequency domain using the pilot signal inserted for each transmission antenna.

  FIG. 5 is a diagram illustrating a configuration example of the channel estimation unit 106 for obtaining the channel gain of the transmission antenna m in the reception antenna n.

  The channel estimation unit 106 illustrated in FIG. 5 includes a DFT unit 131, a transmission / reception filter 132, a reference signal generation unit 133, a correlation processing unit 134, and a noise suppression unit 135. The DFT unit 131 performs DFT on the pilot code of the transmission antenna m and converts it to a frequency domain signal. The transmission / reception filter 132 passes the frequency domain signal of the pilot code through the transmission / reception filter. The reference signal generation unit 133 uses the output of the transmission / reception filter 132 to calculate a pilot reference signal used for correlation processing with the received pilot signal. Correlation processing section 134 estimates the channel gain by correlation processing between the pilot reception signal in the frequency domain and the pilot reference signal. The noise suppression unit 135 suppresses the noise of the channel gain estimated by the correlation processing unit 134 and improves the signal power to noise power ratio (S / N ratio) of the channel estimation value that is the estimated channel gain. As the noise suppression unit 135, a method of averaging adjacent subcarriers, a method of once converting a channel estimation value into the time domain by IDFT, removing a noise path, and returning to the frequency domain by DFT are considered. The channel estimation unit 106 having the configuration shown in FIG. 5 is performed by frequency domain signal processing, but can also be performed by time domain signal processing prior to the DFT units 103-1 to 103 -N.

  The weight calculation unit 107 calculates the weight of the two-dimensional frequency domain equalization using the channel estimation value between the transmission antenna and the reception antenna. The weight calculation unit 107 generally uses an MMSE algorithm. I-th repeated MMSE weight of transmit antenna m

は、チャネル推定値行列

Is the channel estimate matrix

と雑音電力

And noise power

を用いて、次式で計算される。

Is calculated by the following equation.

ここで、

here,

である。また、

It is. Also,

は、送信アンテナｍと受信アンテナとの間のチャネル推定値である。

Is the channel estimate between the transmit antenna m and the receive antenna.

は、送信アンテナｍの第ｉ繰り返し干渉除去考慮行列であり、次式で表される。

Is an i-th iterative interference cancellation consideration matrix of the transmission antenna m, and is expressed by the following equation.

ここで、

here,

は、例えば、送信アンテナｍの時間領域の第ｉ繰り返し軟判定シンボルレプリカ

Is, for example, the i-th iterative soft decision symbol replica in the time domain of the transmission antenna m.

の平均電力を用いて次式で計算される。

Using the average power of

ここで、

here,

は、データブロックのシンボル数である。

Is the number of symbols in the data block.

  The two-dimensional frequency domain equalization unit 108 receives the two-dimensional equalization weight calculated by the weight calculation unit 107 and the output of the subtraction unit 105, and multiplies them for each subcarrier to thereby generate a MIMO signal in the frequency domain. Separation and multipath interference suppression are performed simultaneously. The weight calculated by the weight calculator 107

とし、また、減算部１０５の出力を

And the output of the subtractor 105 is

とすると、２次元周波数領域等化部１０８にて２次元等化された送信アンテナｍの等化信号

Then, the equalized signal of the transmission antenna m that has been two-dimensionally equalized by the two-dimensional frequency domain equalization unit 108

は、次式で表される。

Is expressed by the following equation.

ＩＤＦＴ部１０９−１〜１０９−Ｍは、２次元周波数領域等化部１０８の出力である各送信アンテナの等化信号を入力とし、

The IDFT units 109-1 to 109-M receive the equalized signals of the respective transmitting antennas that are the output of the two-dimensional frequency domain equalizing unit 108 as inputs.

ポイントのＩＤＦＴを行い、等化信号を時間領域に変換する。ＩＤＦＴ部１０９−１〜１０９−Ｍの第ｉ繰り返し（ｉ≧１）の出力が最終的な復調信号となる。

IDFT of points is performed and the equalized signal is converted to the time domain. The output of the i-th repetition (i ≧ 1) of the IDFT units 109-1 to 109-M is the final demodulated signal.

  Bit likelihood calculation sections 110-1 to 110-M calculate the likelihood for each bit transmitted from the equalized signal of each transmission antenna. The bit likelihood calculation units 110-1 to 110-M include a case where a bit is hard-decided.

  Symbol replica generation sections 111-1 to 111 -M generate a symbol replica of transmission antenna m from the likelihood of bits transmitted from each transmission antenna. In the symbol replica generation units 111-1 to 111 -M, a method for generating a hard decision symbol replica, a method for generating a hard decision symbol replica, and multiplying by a predetermined replica weight coefficient (a constant equal to or less than 1), a soft decision symbol A method of generating a replica is used. In particular, the method of generating a soft decision symbol replica has good characteristics.

  The DFT units 112-1 to 112 -M receive the symbol replicas of the transmission antennas generated by the symbol replica generation units 111-1 to 111 -M as inputs,

ポイントのＤＦＴを行い、シンボルレプリカを周波数領域に変換する。

DFT of points is performed to convert the symbol replica to the frequency domain.

  Antenna interference replica generation sections 113-1 to 113-M generate transmission antenna interference replicas using the frequency domain symbol replica signals and channel estimation values of the respective transmission antennas. The symbol replica signal in the frequency domain of the transmitting antenna m

とし、また、チャネル推定値を

And the channel estimate is

とすると、送信アンテナｍの第ｉ繰り返し干渉レプリカ

Then, the i th repetitive interference replica of the transmitting antenna m

は、次式で表される。

Is expressed by the following equation.

以上に述べたように、従来のＭＩＭＯ受信装置では、２次元周波数領域等化とアンテナ干渉除去をチャネル推定も含めて周波数領域で行うことにより、時間領域の信号処理と比べ演算量を大幅に削減するとともに、タイミング誤差の影響を受けないという特徴がある。

As described above, the conventional MIMO receiver significantly reduces the amount of computation compared to time domain signal processing by performing two-dimensional frequency domain equalization and antenna interference cancellation in the frequency domain including channel estimation. In addition, there is a feature that it is not affected by timing errors.

  However, the conventional MIMO receiver continues linear processing without changing the time direction in repeated reception processing of two-dimensional frequency domain equalization and antenna interference cancellation, and the weight after convergence of two-dimensional frequency domain equalization is demodulated. There is a problem that the MMSE weight is applied to the target transmission antenna signal, and noise enhancement due to equalization remains even if repeated. Therefore, it does not reach the reception characteristics of MLD with the best characteristics.

  In order to solve the above-described problems, the present invention converts a single carrier MIMO signal into a frequency domain signal and performs MIMO signal separation by frequency domain processing before performing two-dimensional frequency domain equalization. Computation amount of weight calculation for antenna interference removal and two-dimensional frequency domain equalization by removing all antenna interference replicas and adding a distortion-free signal replica for each transmission antenna after two-dimensional frequency domain equalization In addition to interference with other antennas, multipath interference of a transmission antenna to be demodulated can be removed, and therefore, an object of the present invention is to provide a MIMO reception apparatus and reception method that can realize excellent MIMO reception characteristics.

In order to achieve the above object, the present invention provides:
A MIMO receiver that receives a single-carrier signal transmitted from a plurality of transmission antennas provided in a transmission device by a plurality of reception antennas and separates the signal by a frequency domain,
A DFT unit for performing a discrete Fourier transform on a signal received by the receiving antenna at a first point;
A channel estimation unit that estimates a channel gain between the transmission antenna and the reception antenna using a pilot signal inserted in a signal transmitted from the transmission antenna;
A replica reproducing unit that performs two-dimensional frequency domain equalization based on the weight calculated using the channel gain, and generates an interference replica and an undistorted signal replica of each transmission antenna;
A subtractor for removing the interference replicas of all transmitting antennas from the signal subjected to discrete Fourier transform in the DFT unit;
The signal from which the interference replica has been removed is subjected to two-dimensional frequency domain equalization based on the weight calculated based on the interference removal of the subtracting unit using the channel gain, and the undistorted signal replica is applied to the equalized signal. A demodulator that adds and demodulates the signal transmitted from the transmitting antenna.

  The replica reproduction unit further includes a plurality of subtraction units and a plurality of replica reproduction units, and repeatedly performs antenna interference removal and replica reproduction processing.

  Further, the transmission antenna signal is simultaneously demodulated, and antenna interference is removed in parallel.

  The transmission antenna signal is ordered based on the reception quality, demodulated from the transmission antenna signal with good quality, and antenna interference is sequentially removed.

In addition, the replica reproduction unit
A weight calculation unit for calculating a weight of two-dimensional frequency domain equalization using a channel estimation value between the transmission antenna and the reception antenna;
A two-dimensional frequency domain equalization unit that receives the weight and the signal output from the subtraction unit and multiplies each of the signals for each subcarrier to perform MIMO signal separation and multipath interference suppression in the frequency domain and output the result. When,
An IDFT unit that performs a discrete inverse Fourier transform on a demodulated signal of each transmission antenna, which is a signal output from the two-dimensional frequency domain equalization unit, at a second point;
A bit likelihood calculation unit that calculates a bit likelihood for each transmitted bit based on a demodulated signal of each transmission antenna;
A symbol replica generation unit that generates a symbol replica based on the bit likelihood;
A DFT unit for performing a discrete Fourier transform on the symbol replica at a third point;
An antenna interference replica generation unit that generates a transmission antenna interference replica using a frequency domain symbol replica signal and a channel estimation value;
And a distortion-free signal replica generation unit that generates a distortion-free signal replica by using the frequency domain symbol replica signal and a subcarrier average value of channel gain after two-dimensional frequency domain equalization.

In addition, the demodulation unit
A weight calculation unit that calculates a weight of two-dimensional frequency domain equalization based on interference removal of the subtraction unit using a channel estimation value between the transmission antenna and the reception antenna;
A two-dimensional frequency domain equalization unit that receives the weight and the signal output from the subtraction unit and multiplies each of the signals for each subcarrier to perform MIMO signal separation and multipath interference suppression in the frequency domain and output the result. When,
An adder for adding a distortion-free signal replica to the signal output from the two-dimensional frequency domain equalization unit;
And an IDFT unit that performs discrete inverse Fourier transform on a demodulated signal of each transmitting antenna, which is a signal output from the adding unit, at a second point.

Further, the plurality of replica reproduction units provided in the subsequent stage of the replica reproduction unit,
A weight calculation unit that calculates a weight of two-dimensional frequency domain equalization based on interference removal of the subtraction unit using a channel estimation value between the transmission antenna and the reception antenna;
A two-dimensional frequency domain equalization unit that receives the weight and the signal output from the subtraction unit and multiplies each of the signals for each subcarrier to perform MIMO signal separation and multipath interference suppression in the frequency domain and output the result. When,
An adder for adding a distortion-free signal replica to the signal output from the two-dimensional frequency domain equalization unit;
An IDFT unit that performs a discrete inverse Fourier transform on a demodulated signal of each transmitting antenna, which is a signal output from the adding unit, at a second point;
A bit likelihood calculation unit that calculates a bit likelihood for each transmitted bit based on a demodulated signal of each transmission antenna;
A symbol replica generation unit that generates a symbol replica based on the bit likelihood;
A DFT unit for performing a discrete Fourier transform on the symbol replica at a third point;
An antenna interference replica generation unit that generates a transmission antenna interference replica using a frequency domain symbol replica signal and a channel estimation value;
And a distortion-free signal replica generation unit that generates a distortion-free signal replica by using the frequency domain symbol replica signal and a subcarrier average value of channel gain after two-dimensional frequency domain equalization.

  The replica reproduction unit further includes a decoding unit after the bit likelihood calculation unit, and generates a symbol replica using the bits subjected to error correction decoding.

  Further, the plurality of replica reproduction units provided at the subsequent stage of the replica reproduction unit further include a decoding unit at the subsequent stage of the bit likelihood calculating unit, and generate a symbol replica using the error-corrected decoded bits. And

Also, a MIMO reception method for receiving single-carrier signals transmitted from a plurality of transmission antennas at a plurality of reception antennas and separating the signals by frequency domain processing,
A process of performing a discrete Fourier transform on a signal received by the receiving antenna at a first point;
A process of estimating a channel gain between the transmitting antenna and the receiving antenna using a pilot signal inserted in a signal transmitted from the transmitting antenna;
Performing two-dimensional frequency domain equalization based on the weight calculated using the channel gain, and generating an interference replica and an undistorted signal replica of each transmission antenna;
Removing the interference replicas of all transmit antennas from the discrete Fourier transformed signal;
A process of performing two-dimensional frequency domain equalization using a weight calculated based on interference cancellation of the subtraction unit using the channel gain for the signal from which the interference replica has been removed;
And a process of demodulating the signal transmitted from the transmitting antenna by adding the undistorted signal replica to the equalized signal.

In the present invention configured as described above, in a MIMO receiver in which (deleted) single carrier signals transmitted from a plurality of transmitting antennas are received by a plurality of receiving antennas, and the signals are separated by a frequency domain A non-distorted signal replica in which the antenna interference replica is removed from the received signal before the two-dimensional frequency domain equalization is performed and the antenna interference replica is removed after the two-dimensional frequency domain equalization is performed. Is added.

  Therefore, it is possible to reduce the amount of calculation of weight calculation between antenna interference removal and two-dimensional frequency domain equalization, and it is possible to remove not only interference due to other antennas but also multipath interference of a transmission antenna to be demodulated.

As described above, in the present invention, a MIMO receiving apparatus that receives (deleted) single carrier signals transmitted from a plurality of transmitting antennas at a plurality of receiving antennas and separates the signals in the frequency domain is two-dimensional. A configuration in which an antenna interference replica is removed from a received signal before performing frequency domain equalization, and an undistorted signal replica is added to the signal from which the antenna interference replica has been removed after performing two-dimensional frequency domain equalization; Therefore, excellent MIMO reception characteristics can be realized.

It is a figure which shows the example of 1 structure of the conventional MIMO transmission / reception system using MIMO multiplexing. It is a figure which shows the example of 1 structure of the conventional MIMO receiver. It is a figure which shows an example of the radio | wireless frame format in the case of using frequency domain equalization. It is a figure which shows the example of 1 structure of the subtraction part with respect to the DFT signal of the receiving antenna n. It is a figure which shows the example of 1 structure of the channel estimation part which calculates | requires the channel gain of the transmission antenna m in the receiving antenna n. It is a figure which shows 1st Embodiment of the MIMO receiver of this invention. It is a figure which shows 2nd Embodiment of the MIMO receiver of this invention. It is a figure which shows the form which combined 1st Embodiment shown in FIG. 6 and 2nd Embodiment shown in FIG. It is a figure which shows the structure of the subtraction part with respect to the DFT signal of the receiving antenna n.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 6 is a diagram illustrating a first embodiment of the MIMO receiving apparatus of the present invention.

  As shown in FIG. 6, the MIMO receiving apparatus according to the present embodiment transmits N single carrier MIMO signals transmitted from M (M is an integer of 2 or more) transmission antennas to N (N is an integer of 2 or more) receiving antennas. Is a MIMO receiver that performs MIMO signal separation by frequency domain processing. This MIMO receiving apparatus includes receiving antennas 1-1 to 1-N, a DFT unit 51, a channel estimation unit 52, a replica reproduction unit 53, a subtraction unit 54, and a demodulation unit 55.

  The DFT unit 51 is a first point for signals received by the receiving antennas 1-1 to 1-N.

ポイントでＤＦＴする。チャネル推定部５２は、各送信アンテナから送信された信号に挿入されているパイロット信号を用いて送信アンテナと受信アンテナとの間のチャネル利得を推定する。レプリカ再生部５３は、チャネル利得を用いて計算されたウエイトに基づいて２次元周波数領域等化を行うとともに、各送信アンテナの干渉信号を模した干渉レプリカと歪みの無い信号を模した無歪信号レプリカとを生成する。減算部５４は、ＤＦＴ部５１から出力された信号から全ての送信アンテナの干渉レプリカを除去する。復調部５５は、干渉レプリカを除去された信号についてチャネル利得を用いて減算部５４の干渉除去に基づいて計算されたウエイトにより２次元周波数領域等化を行い、等化された信号に無歪信号レプリカを加算して各送信アンテナ信号を復調する。

DFT with points. The channel estimation unit 52 estimates the channel gain between the transmission antenna and the reception antenna using the pilot signal inserted in the signal transmitted from each transmission antenna. The replica reproducing unit 53 performs two-dimensional frequency domain equalization based on the weight calculated using the channel gain, and also includes an interference replica that imitates an interference signal of each transmitting antenna and an undistorted signal that imitates a signal without distortion. Generate a replica. The subtraction unit 54 removes interference replicas of all transmission antennas from the signal output from the DFT unit 51. The demodulating unit 55 performs two-dimensional frequency domain equalization on the signal from which the interference replica has been removed using the channel gain and based on the weight calculated based on the interference removal by the subtracting unit 54, and the equalized signal is subjected to a distortion-free signal. Add replicas to demodulate each transmit antenna signal.

  The MIMO receiving apparatus according to the present embodiment has a configuration in which the interference replicas of all the transmission antennas are removed by the subtracting unit 54, and the undistorted signal replica is added to each transmission antenna signal after the two-dimensional frequency domain equalization by the demodulating unit 55. As a result, it is possible to eliminate not only other antenna interference but also multipath interference of the transmission antenna to be demodulated. Therefore, excellent MIMO reception characteristics can be realized without increasing the amount of calculation conventionally.

  FIG. 7 is a diagram showing a second embodiment of the MIMO receiving apparatus of the present invention.

  As shown in FIG. 7, the MIMO receiving apparatus according to the present embodiment is further provided with K stages (K is an integer of 1 or more) of subtracting units 56-1 after the replica reproducing unit 53 of the first embodiment shown in FIG. To 56-K and replica reproduction units 57-1 to 57-K. The MIMO receiver shown in FIG. 7 receives single carrier MIMO signals transmitted from M (M is an integer of 2 or more) transmission antennas by N (N is an integer of 2 or more) receiving antennas, A MIMO receiver that performs MIMO signal separation by frequency domain processing. This MIMO receiving apparatus includes reception antennas 1-1 to 1-N, a DFT unit 51, a channel estimation unit 52, a replica reproduction unit 53, subtraction units 56-1 to 56-K, and a replica reproduction unit 57-. 1 to 57-K, a subtractor 54, and a demodulator 55.

  The DFT unit 51 is a first point for signals received by the receiving antennas 1-1 to 1-N.

ポイントでＤＦＴする。チャネル推定部５２は、各送信アンテナから送信された信号に挿入されているパイロット信号を用いて送信アンテナと受信アンテナとの間のチャネル利得を推定する。レプリカ再生部５３は、チャネル利得を用いて計算されたウエイトに基づいて２次元周波数領域等化を行うとともに、各送信アンテナの干渉レプリカと無歪信号レプリカとを生成する。減算部５６−１〜５６−Ｋは、ＤＦＴ部５１から出力された信号から全ての送信アンテナの干渉レプリカをそれぞれ除去する。レプリカ再生部５７−１〜５７−Ｋは、チャネル利得から減算部５６−１〜５６−Ｋの干渉除去を考慮して計算されたウエイトにより２次元周波数領域等化をそれぞれ行う。そして、その出力に無歪信号レプリカを加算して各送信アンテナ信号を復調するとともに、各送信アンテナの干渉レプリカと無歪信号レプリカとを生成する。減算部５４は、ＤＦＴ部５１から出力された信号から全ての送信アンテナの干渉レプリカを除去する。復調部５５は、干渉レプリカを除去された信号についてチャネル利得を用いて減算部５４の干渉除去に基づいて計算されたウエイトにより２次元周波数領域等化を行い、等化された信号に無歪信号レプリカを加算して各送信アンテナ信号を復調する。

DFT with points. The channel estimation unit 52 estimates the channel gain between the transmission antenna and the reception antenna using the pilot signal inserted in the signal transmitted from each transmission antenna. The replica reproducing unit 53 performs two-dimensional frequency domain equalization based on the weight calculated using the channel gain, and generates an interference replica and an undistorted signal replica of each transmission antenna. Subtraction units 56-1 to 56-K remove interference replicas of all transmission antennas from the signal output from DFT unit 51, respectively. The replica reproducing units 57-1 to 57-K perform two-dimensional frequency domain equalization using weights calculated from the channel gain in consideration of the interference removal of the subtracting units 56-1 to 56-K. Then, an undistorted signal replica is added to the output to demodulate each transmitting antenna signal, and an interference replica and an undistorted signal replica of each transmitting antenna are generated. The subtraction unit 54 removes interference replicas of all transmission antennas from the signal output from the DFT unit 51. The demodulating unit 55 performs two-dimensional frequency domain equalization on the signal from which the interference replica has been removed using the channel gain and based on the weight calculated based on the interference removal by the subtracting unit 54, and the equalized signal is subjected to a distortion-free signal. Add replicas to demodulate each transmit antenna signal.

  In the MIMO receiving apparatus according to the present embodiment, subtraction units 56-1 to 56-K and subtraction unit 54 remove interference replicas of all transmission antennas, and replica reproduction units 57-1 to 57-K and demodulation unit 55 A configuration is adopted in which an undistorted signal replica is added to each transmit antenna signal after dimensional frequency domain equalization. As a result, not only other antenna interference but also multipath interference of the transmission antenna to be demodulated can be removed, so that excellent MIMO reception characteristics can be realized without increasing the amount of calculation compared to the conventional one. Also, it is possible to further improve the MIMO reception characteristics by performing highly accurate replica generation by repeatedly performing antenna interference removal and replica reproduction processing.

  Next, detailed operation of the MIMO receiving apparatus of the present invention will be described with reference to FIG.

  FIG. 8 is a diagram showing a form in which the first embodiment shown in FIG. 6 and the second embodiment shown in FIG. 7 are combined.

  As shown in FIG. 8, the MIMO receiving apparatus in this embodiment includes receiving antennas 1-1 to 1-N, CP removing units 2-1 to 2-N, DFT units 3-1 to 3-N, and a receiving filter. 4-1 to 4-N, a subtracting unit 5, a channel estimating unit 6, a weight calculating unit 7, a two-dimensional frequency domain equalizing unit 8, an adding unit 9, and IDFT units 10-1 to 10-M. Bit likelihood calculation units 11-1 to 11-M, symbol replica generation units 12-1 to 12-M, DFT units 13-1 to 13-M, and antenna interference replica generation units 14-1 to 14 -M and distortion-free signal replica generation units 15-1 to 15-M.

  The receiving antennas 1-1 to 1-N receive a single carrier MIMO signal. CP removing sections 2-1 to 2-N receive signals received by the respective receiving antennas 1-1 to 1-N, and remove a signal corresponding to the CP at a common timing. The DFT units 3-1 to 3-N receive the reception antenna signals from which the CP has been removed, and are the first points.

ポイントのＤＦＴを行い、受信信号を周波数領域に変換する。受信フィルタ４−１〜４−Ｎは、周波数領域で受信信号のフィルタリングを行い、波形整形、雑音抑圧、ユーザ分離などを行う。受信フィルタ４−１〜４−Ｎには、一般にレイズドコサインロールオフフィルタが用いられる。図８に示した構成においては、受信フィルタ４−１〜４−Ｎは、周波数領域の信号処理で行っているが、ＤＦＴ部３−１〜３−Ｎに先立ち時間領域の信号処理で行うこともできる。減算部５は、復調対象の送信アンテナ信号も含め、全ての送信アンテナ干渉レプリカを減算する。

A point DFT is performed to convert the received signal into the frequency domain. The reception filters 4-1 to 4-N perform reception signal filtering in the frequency domain, and perform waveform shaping, noise suppression, user separation, and the like. A raised cosine roll-off filter is generally used for the reception filters 4-1 to 4-N. In the configuration shown in FIG. 8, the reception filters 4-1 to 4-N are performed by frequency domain signal processing, but are performed by time domain signal processing prior to the DFT units 3-1 to 3-N. You can also. The subtraction unit 5 subtracts all transmission antenna interference replicas including the transmission antenna signal to be demodulated.

  FIG. 9 is a diagram illustrating a configuration of the subtracting unit 5 for the DFT signal of the receiving antenna n.

  The subtracting unit 5 shown in FIG. 9 includes a replica combining unit 21 and a subtracter 22. The replica combining unit 21 combines all transmission antenna interference replicas. The subtracter 22 subtracts the output of the replica combining unit 21 from the DFT signal of the receiving antenna n. Subcarrier after DFT

の受信信号を

Received signal

とし、また、送信アンテナｍの第ｉ繰り返し干渉レプリカを

And the i th iterative interference replica of the transmitting antenna m

とすると、第ｉ繰り返し干渉除去後の各送信アンテナの等化用信号

Then, the equalization signal of each transmitting antenna after the i-th repetitive interference cancellation

は全ての送信アンテナに対して共通となり次式で表される。

Is common to all transmit antennas and is given by:

ここで、最初（第０繰り返し）の受信処理では干渉除去は行わず、受信信号をそのまま用いる。すなわち、

Here, in the first (0th iteration) reception process, interference is not removed and the received signal is used as it is. That is,

となる。式（９）のアンテナ干渉除去の計算は各送信アンテナに対して共通であるため、従来のものと比べ演算量を削減できる。

It becomes. Since the calculation of the antenna interference removal of Expression (9) is common to each transmission antenna, the calculation amount can be reduced as compared with the conventional one.

  The channel estimation unit 6 estimates a channel gain between the transmission antenna and the reception antenna in the frequency domain using a pilot signal inserted in a signal transmitted from each transmission antenna. In the present embodiment, the channel estimation unit 6 is performed by frequency domain signal processing, but can also be performed by time domain signal processing prior to the DFT units 3-1 to 3-N.

  The weight calculation unit 7 calculates the weight of the two-dimensional frequency domain equalization using the channel estimation value that is the channel gain between the transmission antenna and the reception antenna estimated by the channel estimation unit 6. The weight calculation unit 7 generally uses an MMSE algorithm. I-th repeated MMSE weight of transmit antenna m

は、チャネル推定値行列

Is the channel estimate matrix

と雑音電力

And noise power

とを用いて、次式で計算される。

And is calculated by the following equation.

ここで、

here,

である。また、

It is. Also,

は、送信アンテナｍと受信アンテナとの間のチャネル推定値である。

Is the channel estimate between the transmit antenna m and the receive antenna.

は、第ｉ繰り返し干渉除去考慮行列であり、全ての送信アンテナに対して共通となり次式で表される。

Is the i-th iterative interference cancellation consideration matrix, which is common to all transmission antennas and is expressed by the following equation.

ここで、

here,

は、例えば、送信アンテナｍの時間領域の第ｉ繰り返し軟判定シンボルレプリカ

Is, for example, the i-th iterative soft decision symbol replica in the time domain of the transmission antenna m.

の平均電力を用いて次式で計算される。

Using the average power of

ここで、

here,

は、データブロックのシンボル数である。式（１１）のウエイト計算において逆行列［ ］^−１の計算は送信アンテナｍに対して共通であり１度だけ行えばよく、従来のものと比べ演算量を削減できる。

Is the number of symbols in the data block. In the weight calculation of Expression (11), the calculation of the inverse matrix [] ⁻¹ is common to the transmission antenna m and only needs to be performed once, and the amount of calculation can be reduced compared to the conventional one.

  The two-dimensional frequency domain equalization unit 8 receives the two-dimensional equalization weight calculated by the weight calculation unit 7 and the output of the subtraction unit 5 and multiplies them for each subcarrier to thereby generate a MIMO signal in the frequency domain. Separate and multipath interference suppression are performed simultaneously and output. The weight calculated by the weight calculator 7

とし、また、減算部５の出力を

And the output of the subtracting unit 5 is

とすると、２次元周波数領域等化部８で２次元等化した送信アンテナｍの等化信号

Then, the equalized signal of the transmission antenna m that has been two-dimensionally equalized by the two-dimensional frequency domain equalization unit 8

は、次式で表される。

Is expressed by the following equation.

加算部９は、各送信アンテナの等化信号に無歪信号レプリカを加算して出力する。送信アンテナｍの無歪信号レプリカを

The adder 9 adds an undistorted signal replica to the equalized signal of each transmission antenna and outputs the result. Undistorted signal replica of transmitting antenna m

とすると、送信アンテナｍの第ｉ繰り返し復調信号

Then, the i-th repeated demodulated signal of the transmitting antenna m

は、次式で表される。

Is expressed by the following equation.

式（１６）の処理は従来のものにはなく、演算量の増加となるが、送信アンテナ毎の加算処理であるため、式（９）の減算処理と合わせても、従来の減算処理と比べて演算量は少ない。

The processing of equation (16) is not conventional and increases the amount of calculation. However, since it is an addition processing for each transmission antenna, the subtraction processing of equation (9) is also compared with the conventional subtraction processing. The amount of computation is small.

  The IDFT units 10-1 to 10-M receive the demodulated signal of each transmitting antenna, which is the output of the adding unit 9, and are the second point.

ポイントのＩＤＦＴを行い、復調信号を時間領域に変換する。ＩＤＦＴ部１０−１〜１０−Ｍの第ｉ繰り返し（ｉ≧１）の出力が最終的な復調信号となる。

Point IDFT is performed to convert the demodulated signal into the time domain. The output of the i-th repetition (i ≧ 1) of the IDFT units 10-1 to 10-M is the final demodulated signal.

  The bit likelihood calculation units 11-1 to 11-M calculate the likelihood for each bit transmitted based on the demodulated signal of each transmission antenna. The bit likelihood calculation units 11-1 to 11-M include cases where the bits are hard-decided.

  The symbol replica generation units 12-1 to 12-M generate a symbol replica of the transmission antenna m based on the bit likelihood of the bits transmitted from each transmission antenna. The symbol replica generation units 12-1 to 12-M include a method for generating a hard decision symbol replica, a method for generating a hard decision symbol replica, and multiplying by a predetermined replica weight coefficient (a constant equal to or less than 1), a soft decision symbol A method of generating a replica is used. Further, in the configuration shown in FIG. 8, a symbol replica is generated from the demodulated bits, but error correction is performed after the bit likelihood calculation units 11-1 to 11-N in order to generate a highly accurate replica. A method of generating a symbol replica using a bit provided with a decoding unit that performs decoding and error-correction decoding by the decoding unit is also conceivable.

  The DFT units 13-1 to 13-M receive the symbol replicas of the respective transmission antennas generated by the symbol replica generation units 12-1 to 12-M and are the third points.

ポイントのＤＦＴを行い、シンボルレプリカを周波数領域に変換する。

DFT of points is performed to convert the symbol replica to the frequency domain.

  The antenna interference replica generation units 14-1 to 14-M generate transmission antenna interference replicas using the frequency domain symbol replica signal and the channel estimation value of each transmission antenna. The symbol replica signal in the frequency domain of the transmitting antenna m

とし、またチャネル推定値を

And the channel estimate is

とすると、送信アンテナｍの第ｉ繰り返し干渉レプリカ

Then, the i th repetitive interference replica of the transmitting antenna m

は、次式で表される。

Is expressed by the following equation.

無歪信号レプリカ生成部１５−１〜１５−Ｍは、各送信アンテナの周波数領域のシンボルレプリカ信号と２次元周波数領域等化後のチャネル利得のサブキャリア平均値とを用いて無歪信号レプリカを生成する。送信アンテナｍの周波数領域のシンボルレプリカ信号を

The distortion-free signal replica generation units 15-1 to 15-M generate distortion-free signal replicas by using the frequency domain symbol replica signals of each transmission antenna and the channel gain subcarrier average value after two-dimensional frequency domain equalization. Generate. The symbol replica signal in the frequency domain of the transmitting antenna m

とし、また、等化後チャネル利得のサブキャリア平均値を

And the subcarrier average value of the channel gain after equalization is

とすると、送信アンテナｍの第ｉ繰り返し無歪信号レプリカ

And the i-th iterative undistorted signal replica of the transmitting antenna m

は、次式で表される。

Is expressed by the following equation.

ここで、

here,

以上説明した第１の実施の形態および第２の実施の形態において、アンテナ干渉除去とレプリカ再生との各繰り返し処理では各送信アンテナ信号を同時に復調し、アンテナ干渉レプリカを並列的に除去している。各繰り返し処理で送信アンテナ信号を受信品質に基づきオーダリングし、品質の良い送信アンテナ信号から復調し、アンテナ干渉を逐次的に除去する方法も考えられる。具体的には、最初（第０繰り返し）の受信処理では受信品質のよい送信アンテナ信号から順番に復調し、ＤＦＴ信号から干渉レプリカを除去していく。第ｉ繰り返し（ｉ≧１）の受信処理ではＤＦＴ信号から前の繰り返しの全ての送信アンテナ干渉を除去した受信信号から受信品質のよい送信アンテナ信号の順番に今回の干渉レプリカと前回の干渉レプリカとの差分を除去していく。この場合、送信アンテナ信号の逐次干渉除去の効果により繰り返し数に対する受信特性は良くなるが、送信アンテナ毎にアンテナ干渉除去と２次元周波数領域等化のウエイト計算とを行う必要があり演算量が増加する。

In the first embodiment and the second embodiment described above, in each iterative process of antenna interference removal and replica reproduction, each transmission antenna signal is simultaneously demodulated, and antenna interference replicas are removed in parallel. . A method is also conceivable in which the transmission antenna signal is ordered based on the reception quality in each iterative process, demodulated from a high-quality transmission antenna signal, and antenna interference is sequentially removed. Specifically, in the first (0th repetition) reception process, demodulation is performed in order from a transmission antenna signal having good reception quality, and interference replicas are removed from the DFT signal. In the i-th iterative (i ≧ 1) reception process, the current interference replica and the previous interference replica are arranged in the order of the transmission antenna signal having good reception quality from the reception signal from which all the transmission antenna interference of the previous repetition has been removed from the DFT signal. The difference is removed. In this case, the reception characteristic with respect to the number of repetitions is improved due to the effect of successive interference cancellation of the transmission antenna signal, but the amount of calculation increases because it is necessary to perform antenna interference cancellation and weight calculation for two-dimensional frequency domain equalization for each transmission antenna. To do.

  In the present embodiment, the conversion from the time domain signal to the frequency domain signal is performed by DFT, and the conversion from the frequency domain signal to the time domain signal is performed by IDFT, but fast Fourier transform (FFT) is used. ), Inverse Fast Fourier Transform (IFFT) or other algorithms may be used.

Claims (10)

A MIMO receiver that receives a single carrier signal transmitted from a plurality of transmitting antennas at a plurality of receiving antennas and separates the signal by a frequency domain,
A DFT unit for performing a discrete Fourier transform on a signal received by the receiving antenna at a first point;
A channel estimation unit that estimates a channel gain between the transmission antenna and the reception antenna using a pilot signal inserted in a signal transmitted from the transmission antenna;
A replica reproducing unit that performs two-dimensional frequency domain equalization based on the weight calculated using the channel gain, and generates an interference replica and an undistorted signal replica of each transmission antenna;
A subtractor for removing the interference replicas of all transmitting antennas from the signal subjected to discrete Fourier transform in the DFT unit;
The signal from which the interference replica has been removed is subjected to two-dimensional frequency domain equalization based on the weight calculated based on the interference removal of the subtracting unit using the channel gain, and the undistorted signal replica is applied to the equalized signal. A MIMO receiving apparatus comprising: a demodulator that adds and demodulates a signal transmitted from the transmitting antenna.   The MIMO receiving apparatus according to claim 1, further comprising a plurality of subtracting units and a plurality of replica reproducing units after the replica reproducing unit, and repeatedly performing antenna interference removal and replica reproducing processing.   The MIMO receiving apparatus according to claim 1 or 2, wherein the transmitting antenna signal is simultaneously demodulated and antenna interference is removed in parallel.   The MIMO receiving apparatus according to claim 1 or 2, wherein the transmission antenna signal is ordered based on reception quality, demodulated from a high-quality transmission antenna signal, and antenna interference is sequentially removed. The replica reproduction unit
A weight calculation unit for calculating a weight of two-dimensional frequency domain equalization using a channel estimation value between the transmission antenna and the reception antenna;
A two-dimensional frequency domain equalization unit that receives the weight and the signal output from the subtraction unit and multiplies each of the signals for each subcarrier to perform MIMO signal separation and multipath interference suppression in the frequency domain and output the result. When,
An IDFT unit that performs a discrete inverse Fourier transform on a demodulated signal of each transmission antenna, which is a signal output from the two-dimensional frequency domain equalization unit, at a second point;
A bit likelihood calculation unit that calculates a bit likelihood for each transmitted bit based on a demodulated signal of each transmission antenna;
A symbol replica generation unit that generates a symbol replica based on the bit likelihood;
A DFT unit for performing a discrete Fourier transform on the symbol replica at a third point;
An antenna interference replica generation unit that generates a transmission antenna interference replica using a frequency domain symbol replica signal and a channel estimation value;
2. A distortion-free signal replica generation unit that generates a distortion-free signal replica using the frequency domain symbol replica signal and a subcarrier average value of channel gain after two-dimensional frequency domain equalization. The MIMO receiver described in 1. The demodulator
A weight calculation unit that calculates a weight of two-dimensional frequency domain equalization based on interference removal of the subtraction unit using a channel estimation value between the transmission antenna and the reception antenna;
A two-dimensional frequency domain equalization unit that receives the weight and the signal output from the subtraction unit and multiplies each of the signals for each subcarrier to perform MIMO signal separation and multipath interference suppression in the frequency domain and output the result. When,
An adder for adding a distortion-free signal replica to the signal output from the two-dimensional frequency domain equalization unit;
The MIMO receiving apparatus according to claim 1, further comprising: an IDFT unit that performs discrete inverse Fourier transform on a demodulated signal of each transmitting antenna, which is a signal output from the adding unit, at a second point. The plurality of replica reproduction units provided at the subsequent stage of the replica reproduction unit,
A weight calculation unit that calculates a weight of two-dimensional frequency domain equalization based on interference removal of the subtraction unit using a channel estimation value between the transmission antenna and the reception antenna;
A two-dimensional frequency domain equalization unit that receives the weight and the signal output from the subtraction unit and multiplies each of the signals for each subcarrier to perform MIMO signal separation and multipath interference suppression in the frequency domain and output the result. When,
An adder for adding a distortion-free signal replica to the signal output from the two-dimensional frequency domain equalization unit;
An IDFT unit that performs a discrete inverse Fourier transform on a demodulated signal of each transmitting antenna, which is a signal output from the adding unit, at a second point;
A bit likelihood calculation unit that calculates a bit likelihood for each transmitted bit based on a demodulated signal of each transmission antenna;
A symbol replica generation unit that generates a symbol replica based on the bit likelihood;
A DFT unit for performing a discrete Fourier transform on the symbol replica at a third point;
An antenna interference replica generation unit that generates a transmission antenna interference replica using a frequency domain symbol replica signal and a channel estimation value;
3. A distortion-free signal replica generation unit configured to generate a distortion-free signal replica using the frequency domain symbol replica signal and a subcarrier average value of channel gain after two-dimensional frequency domain equalization. The MIMO receiver described in 1.   6. The MIMO receiving apparatus according to claim 5, wherein the replica reproduction unit further includes a decoding unit subsequent to the bit likelihood calculating unit, and generates a symbol replica using bits subjected to error correction decoding.   The plurality of replica reproduction units provided at the subsequent stage of the replica reproduction unit further include a decoding unit at the subsequent stage of the bit likelihood calculating unit, and generate a symbol replica using the bits subjected to error correction decoding The MIMO receiver according to claim 7. A MIMO reception method for receiving signals of a single carrier transmitted from a plurality of transmission antennas at a plurality of reception antennas and separating the signals by frequency domain processing,
A process of performing a discrete Fourier transform on a signal received by the receiving antenna at a first point;
A process of estimating a channel gain between the transmitting antenna and the receiving antenna using a pilot signal inserted in a signal transmitted from the transmitting antenna;
Performing two-dimensional frequency domain equalization based on the weight calculated using the channel gain, and generating an interference replica and an undistorted signal replica of each transmission antenna;
Removing the interference replicas of all transmit antennas from the discrete Fourier transformed signal;
A process of performing two-dimensional frequency domain equalization using a weight calculated based on interference cancellation of the subtraction unit using the channel gain for the signal from which the interference replica has been removed;
And a process of demodulating a signal transmitted from the transmitting antenna by adding the undistorted signal replica to the equalized signal.

Images